Eukaryotic protein translation initiation factor 5A (eIF-5A) contains one residue of hypusine and appears to be the only cellular protein with this unique amino acid. Hypusine is produced post- translationally by transfer of the butylamine portion of the polyamine spermidine to a lysyl residue in the eIF-5A precursor to form deoxyhypusine followed by hydroxylation to form hypusine. In an effort to identify cellular proteins with which eIF-5A interacts to exert its biological activity, we have originated an affinity method for their isolation. Polyhistidine-tagged human eIF- 5A precursor protein (His-tag-ec-eIF-5A) was produced by utilizing pET-24b vector. The deoxyhypusine-containing form was prepared by modification of His-tag-ec-eIF-5A in the deoxyhypusine synthase reaction. The his-tagged proteins bound to a Ni (II)-NTA-agarose column are being used as an affinity matrix to isolate and identify cellular proteins that specifically interact with eIF-5A. Although it is well established that hypusine is vital for eukaryotic cell proliferation, the precise physiological role of the hypusine- containing protein eIF-5A is yet unknown. We are also studying the specific interaction of eIF-5A precursor protein with deoxyhypusine synthase in vitro by the use of His-tag-ec-eIF-5A or His-tag- deoxyhypusine synthase bound to the Ni(II) resin as an affinity matrix. In a recent study from another laboratory, eIF-5A was reported to be a host cellular factor required for Rev function in the replication of HIV-1. We are currently investigating the role of hypusine modification in the interaction of eIF-5A and Rev and the possible intervention of HIV-1 replication through inhibition of hypusine synthesis.